Trace Minerals: What to supplement and when

U.S. cow/calf producers have been faced with an extreme increase in operating costs over the past year, especially for feed and supplements. Thus, even with strong calf prices, profitability can be hard to achieve

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U.S. cow/calf producers have been faced with an extreme increase in operating costs over the past year, especially for feed and supplements. Thus, even with strong calf prices, profitability can be hard to achieve.

One key method for improving profit is to reduce costs without negatively affecting performance – namely through reproduction. To do so, aim for better management of the high-cost trace mineral supplement you are feeding your cows. Let’s take a closer look.

Which trace minerals are most important? Trace minerals are required at concentrations less than 100 parts per million (ppm, also known as mg per kg) of diet. The National Research Council (NRC) has identified 10 trace minerals as essential for beef cattle; however, only about 4 are generally recognized as the most problematic in grazing beef cattle: copper (Cu), zinc (Zn), manganese (Mn), and selenium (Se).

In most herds, trace mineral deficiencies probably don’t exist. However, marginal trace mineral deficiencies do exist and commonly go unnoticed since only slight reductions in performance occur. In some situations, a deficiency can lead to a decrease in performance including reduced growth, body weight, condition scores, and/or milk production, as well as health-related problems.

Trace Mineral Challenges Many forages across the U.S. contain less-than-adequate concentrations of these several trace minerals. The National Animal Health Monitoring Service (NAHMS) reported that Zn was adequate in only 3% of forage samples from across the U.S., and 50% of samples were marginal in Cu. However, Mn was adequate in 76% of samples.

In addition many forage samples contained minerals that are antagonist to trace minerals such as Cu and reduce absorption. This includes minerals like iron (Fe) and molybdenum (Mo). In the NAHMS study, 9% of samples were very high in Mo, which when present with Cu and sulfur (S) form a complex that is almost completely unabsorbable by ruminants. Similarly, 12% of forage samples were very high in Fe which can cause Cu deficiency.

To make matters worse, trace minerals are poorly absorbed by beef cattle since only about 5 to 10% is absorbed. Similarly, several factors affect the efficiency of trace mineral absorption including reproduction and stress. For instance, the requirement for Mn for gestating and early lactating cattle (40 ppm) is twice the requirement for feedlot cattle (20 ppm).

Determining the right supplement Supplementation of trace minerals to beef cattle is common based on the reasons mentioned above. However, anecdotal evidence indicates that many purchased mineral mixes supply trace minerals unnecessarily to cattle, or worse don’t provide enough mineral.

The concentrations which trace minerals should be included in a mineral mix can be determined by comparing the results of a feedstuff analysis with NRC recommended concentrations (Table 2).

If a feedstuff does not meet the concentrations listed in Table 2, trace mineral supplementation is recommended. Ideally, a custom mineral supplement should be developed with the help of a feed store nutritionist; however, this typically requires a minimum order (i.e. 1-2 Tons).

For those of us who are unable to order a custom mix, we may be able to find an appropriate mineral mix at the local feed store. However, the major challenge faced by many producers is determining which one of the “generic” mineral mixes for sale contain enough of these minerals for their cows.

What a mineral mix “should” contain Unfortunately, the label on a bag of mineral mix usually only includes the concentration of minerals actually in the bag – which is very very high since the minerals are concentrated into the bag because cows only consume a small amount each day. However, bag labels also include the average amount of the mineral mix that a cow should eat every day. This is important information, but is often overlooked – especially by producers who provide mineral to their cows based solely on the mineral feeder being empty.

If the label indicates that a cow should consume 4 ounces per day (or 1/4 of a pound), a series of calculations can be done to determine how much of each mineral she will consume. This exercise can be extremely frustrating since the mineral concentration is typically included on the label in metric basis (mg/kg, mg/lb, mg/day, or ppm) while consumption is listed in pounds. This makes converting between the two difficult, to say the least.

The University of Nebraska has a great tool available on their website for producers who would like to figure out exactly what their cows need and how any commercially-available mineral mix will measure up.

Using the Nebraska calculations, it is relatively easy to determine how much of every trace mineral a bag “should” contain to meet cow requirements. Before going through an example, let’s first assume that we weren’t able to analyze our feeds and therefore we must assume that they don’t contain any trace minerals (this is probably not the case, but is our best guess for now).

Let’s also assume that we have a 1,200 lb cow consuming 1/4 lb of a mineral mix daily (based on the bag label’s indication). Using the on-line calculator, her Cu requirement will be met if the mix contains at least 1,000 ppm of Cu. Thus, you should only buy a bag of mineral mix with at least 1,000 ppm of Cu in it, which will meet your cow’s requirements. However, it should be noted that this calculation is based on the assumption that Cu antagonists (Mo, S, and Fe) are not elevated.

Using the same calculations, a mineral mix needs to also contain 3,000 ppm Zn, 4,000 ppm Mn, and 10 ppm Se to meet that cow’s requirements. Again, this is based on “assumptions” for body weight and daily intake. Interestingly, if only 1/8 lb (or 2 ounces) is going to be consumed instead, the concentrations on the label will need to be twice as much. If she consumes half as much of the mix (2 vs. 4 ounces), it must be twice as concentrated and therefore needs to have 2,000 ppm Cu, 6,000 ppm Zn, 8,000 ppm Mn, and 20 ppm Se.

Keep in mind that almost none of the 50 lb salt blocks with trace minerals added to them are able to provide adequate amounts of trace minerals to cattle, with the possible exception of Se (since it is required in such a small concentration). That is why trace minerals are commonly provided as a free-choice loose mineral mix or added to pre-formulated supplements (e.g. protein tubs, blocks, or licks).

It is also important to understand that contrary to popular belief, animals are not able to voluntarily determine which minerals they are lacking, and can’t modify their consumption behavior based on physiological need. Because of this, free-choice loose mineral mixes are used; however, their use depends on voluntary consumption. If daily consumption is different from the label’s recommendation, strategies can be used to limit the intake of a mineral mix such as adding loose salt, moving mineral feeders away from the water source, and reducing the frequency of filling mineral feeders.

The Bottom Line Supplementation of trace minerals can be an area where significant cost can be saved over a cow’s lifetime. Several trace minerals are challenging – including copper, zinc, manganese, and selenium – because they are inadequate in many forages across the U.S. and/or are unavailable to cattle due to the presence of antagonists.

Evaluating both feedstuffs and water for trace mineral concentrations will help to determine whether supplementation is justified. And, in some instances producers should consider tissue collection (such as a liver biopsy sample, by a licensed veterinarian) from a subset of animals to diagnose a possible trace mineral deficiency or toxicity.